Fix ART builbot after hiddenapi files change

hiddenapi tool now produces a single CSV file rather than multiple
text files. Change ART's makefile to create an empty file of the same
name when running on the buildbots.

Test: n/a
Change-Id: I8347cdaefbd4359dc7943293a7eb2a5702105bfa
diff --git a/Android.mk b/Android.mk
index 3388b35..ba131c6 100644
--- a/Android.mk
+++ b/Android.mk
@@ -474,7 +474,7 @@
 define build-art-hiddenapi
 $(shell if [ ! -d frameworks/base ]; then \
   mkdir -p ${TARGET_OUT_COMMON_INTERMEDIATES}/PACKAGING; \
-	touch ${TARGET_OUT_COMMON_INTERMEDIATES}/PACKAGING/hiddenapi-{whitelist,blacklist,dark-greylist,light-greylist}.txt; \
+	touch ${TARGET_OUT_COMMON_INTERMEDIATES}/PACKAGING/hiddenapi-flags.csv; \
   fi;)
 endef